The present invention refers to check valves for medical infusion lines and the like.
Such check (or non return) valves normally comprise a first and a second tubular element that respectively define an upstream and a downstream passageway, mutually coaxial to each other and between which a diaphragm of elastically deformable material is transversely positioned, sealingly cooperating with an annular valve seat of the said first tubular element to form a fluid seal that maintains the check valve in a normally closed position, and in which a predetermined fluid pressure in the said upstream passageway causes a deflection of the diaphragm and consequent opening of the check valve.
Such check valves must meet a series of critical requirements: in the first place, they must normally be closed and must only open, continuously or intermittently, when the pressure in the upstream passageway is higher than a predetermined threshold, normally of small entity e.g. 0.005-0.02 bar. The check valve must also be capable of preventing any reflux from the downstream passageway to the upstream passageway with utmost security, i.e. it must be capable of rapidly closing itself in cases where a minimal overpressure enters the downstream passageway.
Another requirement of the check valves used in the medical applications in question consists in simple and low-cost design, in connection both with manufacturing and assembling of the check valve.
The object of the present invention is to provide a check valve of the above-referenced type wholly fulfilling the aforesaid requirements.
A further object of the present invention is to provide a check valve of the above-referenced type which is simply to adjust, upon manufacturing thereof, as a function of the user""s need.
According to the invention this object is achieved essentially by the fact that the the annular valve seat is defined by a front surface of the first tubular element and the diaphragm consists of the bottom wall of a cup-shaped element coxial with said upstream and downstream passageways, said bottom wall being normally urged into seal contact against said annular valve seat under an axial thrust provided by the lateral wall of said cup-shaped element; deflexion of said bottom wall of said cup-shaped element produced in use by said predetermined fluid pressure causing axial separation thereof relative to said annular valve seat.
By virtue of this solution, in operation opening of the check valve takes place promptly even if the diaphragm constituted by the dome portion of the cup-shaped element is subjected to a relative high axial pre-load so as to ensure the maximum degree of closing safety and reliability. Moreover, in the open condition of the valve any increase of the fluid flow rate will result into a proportionally greater deformation of the bottom wall of the cup-shaped element and, therefore, into a proportionally greater distance of the dome portion relative to the valve seat.